I'm new to the hobby and the forum, and putting together a telescope assembly for viewing the sky. As I am purchasing all the different components with researching as much as I can, and I realize I might need a filter. I plan to (starting off) lean more towards observing galaxies and nebulae. My question is which filter starting off will be good for viewing these objects? From what I am finding, I may need to get an O-III filter or H-Alpha. Or maybe both. I do live in the suburbs. Right now I have or have ordered the following:

I find that filter most useful. I use it a lot during star parties, until I sold it...

The Tele Vue Bandmate OIII is not the best OIII filter around. It has a bandwidth (full-width at Half maximum) of around 241 angstroms, which is as broad as some narrow-band nebula filters. This does not provide quite as much rejection of background skyglow as the narrower "true" OIII filters like those from Lumicon. The DGM Optics NPB filter has a similar FWHM passband width but is designed to also pass the H-Beta nebular emission line as well as the OIII lines, so it will provide superior performance to the Tele Vue "OIII". The Lumicon OIII has a FWHM bandwidth of around 120 angstroms which is less than half that of the Tele Vue OIII. This often makes it more effective in providing increased contrast for certain nebulae, especially when using the filter to "blink" small nearly stellar planetary nebulae in rich star fields. Clear skies to you.

Although it's more ex$pen$ive I heartily recommend the 2" (48mm) NPB to thread into your Type 2 Paracorr. When used with the 31T5 TermiNagler the >2.6° TFoV (if the 6.85mm exit pupil is acceptable) would really go to town on the Veil and North American nebulae, though a 21 Ethos's 2.25° with 4.64mm exit pupil couldn't be called shabby!

Complementing the NPB's extra H-Beta bandwidth, a Lumicon OIII acquired later will add extra detail to many objects, with the H-Beta line filter added last.

I find that filter most useful. I use it a lot during star parties, until I sold it...

The Tele Vue Bandmate OIII is not the best OIII filter around. It has a bandwidth (full-width at Half maximum) of around 241 angstroms, which is as broad as some narrow-band nebula filters. This does not provide quite as much rejection of background skyglow as the narrower "true" OIII filters like those from Lumicon. The DGM Optics NPB filter has a similar FWHM passband width but is designed to also pass the H-Beta nebular emission line as well as the OIII lines, so it will provide superior performance to the Tele Vue "OIII". The Lumicon OIII has a FWHM bandwidth of around 120 angstroms which is less than half that of the Tele Vue OIII. This often makes it more effective in providing increased contrast for certain nebulae, especially when using the filter to "blink" small nearly stellar planetary nebulae in rich star fields. Clear skies to you.

David: Does this mean the DGM NPB filter can be used on H-Beta and OIII objects, sort of an all-in-one filter???
Andy

Dave won't be home till much later - but as we frequently observe together, the short answer is YES.

The DGM NPB filter, (and to a lesser extent many of the Lumicon UHC filters), DO act as a sort of an all-in-one filter. That's one reason the NPB helps for so may objects compared to many other narrowband filters - but most especially compared to NO filter. It can be used for both H-beta and OIII objects. If you can only have one the NPB would be my first choice - especially for "finding" and the public with what is typically a "brighter" view.

However... many nebular views are comprised of OIII AND H-beta lines. The DGM NPB is well suited for viewing the largest variety of nebulae, but when OIII AND H-beta lines are prominent the details can be "muddied" with a filter that passes both.

When the NPB is swapped for an OIII or H-beta line filter, though the view may well be darker, the contrast is improved, and the whole shape of the nebula may change from one filter to the next! In the long run you'll want the NPB, OIII, and H-beta filters. With line filters the lovely knots, striations, and whorls are more readily seen in detail that are difficult or impossible to see with the NPB or a broadband filter like Orion's SkyGlow.

A broadband filter like Orion's SkyGlow also has a place in my toolbox. It's a public favorite (to better see with little or no dark adaptation) on the Great Orion Nebula, and, in dark skies I prefer it to so called "Galaxy Filters".

I find that filter most useful. I use it a lot during star parties, until I sold it...

The Tele Vue Bandmate OIII is not the best OIII filter around. It has a bandwidth (full-width at Half maximum) of around 241 angstroms, which is as broad as some narrow-band nebula filters. This does not provide quite as much rejection of background skyglow as the narrower "true" OIII filters like those from Lumicon. The DGM Optics NPB filter has a similar FWHM passband width but is designed to also pass the H-Beta nebular emission line as well as the OIII lines, so it will provide superior performance to the Tele Vue "OIII". The Lumicon OIII has a FWHM bandwidth of around 120 angstroms which is less than half that of the Tele Vue OIII. This often makes it more effective in providing increased contrast for certain nebulae, especially when using the filter to "blink" small nearly stellar planetary nebulae in rich star fields. Clear skies to you.

David: Does this mean the DGM NPB filter can be used on H-Beta and OIII objects, sort of an all-in-one filter???
Andy

Yes, that is correct. In fact, the NPB is nearly as good as some of the broader OIII filters and even lets me see some H-Beta objects like the Horsehead nebula and the California Nebula. It isn't quite as good as a dedicated OIII or H-Beta filter, but it does work well on a variety of emission nebulae as a "one filter" solution. Clear skies to you.

Hmmm...It's a toss up between my Lumicon UHC and OIII filters. I try both on each object for the best view.

Specifically I cannot see the Veil nebula unless I use the OIII nor can I see the small planetary nebula in Messier 46 without the UHC.

Actually, you will in general need *both* a narrow-band "UHC-like" filter *and* a good Oxygen III filter to cover all the bases when it comes to emission nebulae. If you want to get an idea of which filter works with which objects, the following article may be of some help:

Although it's more ex$pen$ive I heartily recommend the 2" (48mm) NPB to thread into your Type 2 Paracorr. When used with the 31T5 TermiNagler the >2.6° TFoV (if the 6.85mm exit pupil is acceptable) would really go to town on the Veil and North American nebulae, though a 21 Ethos's 2.25° with 4.64mm exit pupil couldn't be called shabby!

Complementing the NPB's extra H-Beta bandwidth, a Lumicon OIII acquired later will add extra detail to many objects, with the H-Beta line filter added last.

I'm glad you mentioned this. I was curious as to what size to get and where to place it with the Paracorr. I can get 2" filters that are threaded to the Paracorr, then any eyepiece either 1.25" or 2" will work with the same 2" filter. Am I thinking about this correctly?

I find that filter most useful. I use it a lot during star parties, until I sold it...

The Tele Vue Bandmate OIII is not the best OIII filter around. It has a bandwidth (full-width at Half maximum) of around 241 angstroms, which is as broad as some narrow-band nebula filters. This does not provide quite as much rejection of background skyglow as the narrower "true" OIII filters like those from Lumicon. The DGM Optics NPB filter has a similar FWHM passband width but is designed to also pass the H-Beta nebular emission line as well as the OIII lines, so it will provide superior performance to the Tele Vue "OIII". The Lumicon OIII has a FWHM bandwidth of around 120 angstroms which is less than half that of the Tele Vue OIII. This often makes it more effective in providing increased contrast for certain nebulae, especially when using the filter to "blink" small nearly stellar planetary nebulae in rich star fields. Clear skies to you.

I'm glad you mentioned this. I was curious as to what size to get and where to place it with the Paracorr. I can get 2" filters that are threaded to the Paracorr, then any eyepiece either 1.25" or 2" will work with the same 2" filter. Am I thinking about this correctly?

Thanks,

You got it! That's how I use it. For nebulae, where low magnification and large TFoV/exit pupil is desirable and 48mm in the Paracorr rules; after I find which filter works best, I'm more likely to be swapping eyepieces to tease out the structure in the knots and whorls. For filters that are only used at higher magnification where a large TFoV/exit pupil doesn't matter like the Moon & planets (Wratten color filters), I $aved money on the 1.25" variety. Once I discover maximum magnification seeing currently allows, I'm more likely to be swapping filters than eyepieces.

You have to be careful with anecdotal evidence and manufacturer specifications. If you are looking at what filter is "better" you really need a comparison of transmittance spectra made with the same spectrophotometer to compare the transmittance at the desired frequencies and rejection at other frequencies *on the same instrument* as they can vary even a few percent. This has not been done for awhile as far as I know with current filters. For subjective observations, one person's opinions are of course statistically worthless. Also it'd be nice to have ASTM tests on the coatings. Now you really hope that given the price of the Lumicon filters for example, that they are the best out there, but we really have nothing to support that beyond their claims do we? So Step 1), someone buy a spectrophotometer or borrow one from work and test all the filters out there please!

You have to be careful with anecdotal evidence and manufacturer specifications. If you are looking at what filter is "better" you really need a comparison of transmittance spectra made with the same spectrophotometer to compare the transmittance at the desired frequencies and rejection at other frequencies *on the same instrument* as they can vary even a few percent. This has not been done for awhile as far as I know with current filters. For subjective observations, one person's opinions are of course statistically worthless. Also it'd be nice to have ASTM tests on the coatings. Now you really hope that given the price of the Lumicon filters for example, that they are the best out there, but we really have nothing to support that beyond their claims do we? So Step 1), someone buy a spectrophotometer or borrow one from work and test all the filters out there please!

Are you responding to me? While quantitative data of filters available for purchase and for reference would be nice to have; it's largely irrelevant when when real question for me is:

"Which of the filters available for use on the equipment at the observing site shows the best qualitative view of the details most desired to be seen in a particular view?"

The answer to THAT question is not always intuitively obvious, even if you do have a list of object characteristics with tables and charts of the various filters available. Not only are viewing conditions and equipment availability subject to change without notice; but so are some of the details an observer might prefer to see. Some nebulae appear very different depending on the filter used - particularly the views with OIIIANDHß lines!

You have to be careful with anecdotal evidence and manufacturer specifications. If you are looking at what filter is "better" you really need a comparison of transmittance spectra made with the same spectrophotometer to compare the transmittance at the desired frequencies and rejection at other frequencies *on the same instrument* as they can vary even a few percent. This has not been done for awhile as far as I know with current filters. For subjective observations, one person's opinions are of course statistically worthless. Also it'd be nice to have ASTM tests on the coatings. Now you really hope that given the price of the Lumicon filters for example, that they are the best out there, but we really have nothing to support that beyond their claims do we? So Step 1), someone buy a spectrophotometer or borrow one from work and test all the filters out there please!

Over about the past 30 years or so, I have observed with filters from sources like Lumicon, Thousand Oaks, Orion, Baader, DGM Optics, Meade, and a few others (some of which are no longer in business). Most of these companies produce decent filters that do work pretty well, although there are definite differences between how some of these filters perform (and it also helps to have a spectroscope/spectrophotometer handy to check on the passbands at least visually). Generally, after extensive observations, I have been pretty satisfied as to the consistency of the filters produced by Lumicon. Until recently, I considered them to be the "gold standard" against which everything else was measured against. When Dan McShane sent me the DGM Optics NPB, I was expecting it to perform about as well as the Lumicon UHC, but I was a little startled to find that I liked the NPB just a bit better than the good old Lumicon UHC:

That one became my favorite narrow-band nebula filter, although again, the difference between it and the Lumicon UHC were fairly minor. Indeed, even the Orion Ultrablock seemed about on-par with the Lumicon UHC, so in these cases, I can recommend buying from one of these three based on price alone. However, that changed with the narrower "line" filters like the OIII. The Tele Vue OIII just didn't quite match the Lumicon OIII's performance, although it still provides a boost in contrast. The DGM OIII was pretty close to the Lumicon model in side-by-side tests, although I still like the Lumicon by a hair, so you really can't go wrong with either one of these two (ditto for the Thousand Oaks OIII Type 3). In fact, in my review tests of the DGM OIII, the DGM NPB narrow-band filter gave the DGM OIII a real run for its money in terms of the amount of contrast boost it provided. The Baader OIII was also good, but perhaps just a hair on the narrow side (cuts into the 4959 angstrom OIII emission line a bit), so again, I tend to fall back on the Lumicon OIII as continuing to be my "gold standard" in Oxygen III filters. These are not "anecdotal" accounts, but the result of some careful study, both spectroscopically and in the field with a slide comparative system. For those filters not on this "short list", well, "ya pays your money and ya takes your chances". I am still pretty confident that the Lumicon line is one of the best sets of filters out there. Clear skies to you.

I still have not picked up the DGM NPB yet, I really like my Lumicon OIII filter as my choice for OIII line filter. I really think you folks out there looking to get a filter you can't go wrong picking up a DGM NPB filter, great price too! You can save a few bucks going this way, as in getting the DGM NPB and down the road grab a good OIII filter like the Lumicon. Don't cut yourself short on the OIII filter, take this from a guy that views from a red zone using it in a 8" Dob. With dark adapted eyes the views with it will knock your socks off, for me just being able to view The Veil alone was worth the purchase.

I was able to see both east and west sections of the Veil in the same field of view in my "Tascostan" 4-1/4" f/4 with a Lumicon UHC in orange skies. I was astounded. Was not visible in that scope without the filter (at least on that night).

You have to be careful with anecdotal evidence and manufacturer specifications. If you are looking at what filter is "better" you really need a comparison of transmittance spectra made with the same spectrophotometer to compare the transmittance at the desired frequencies and rejection at other frequencies *on the same instrument* as they can vary even a few percent. This has not been done for awhile as far as I know with current filters. For subjective observations, one person's opinions are of course statistically worthless. Also it'd be nice to have ASTM tests on the coatings. Now you really hope that given the price of the Lumicon filters for example, that they are the best out there, but we really have nothing to support that beyond their claims do we? So Step 1), someone buy a spectrophotometer or borrow one from work and test all the filters out there please!

Over about the past 30 years or so, I have observed with filters from sources like Lumicon, Thousand Oaks, Orion, Baader, DGM Optics, Meade, and a few others (some of which are no longer in business). Most of these companies produce decent filters that do work pretty well, although there are definite differences between how some of these filters perform (and it also helps to have a spectroscope/spectrophotometer handy to check on the passbands at least visually). Generally, after extensive observations, I have been pretty satisfied as to the consistency of the filters produced by Lumicon. Until recently, I considered them to be the "gold standard" against which everything else was measured against. When Dan McShane sent me the DGM Optics NPB, I was expecting it to perform about as well as the Lumicon UHC, but I was a little startled to find that I liked the NPB just a bit better than the good old Lumicon UHC:

That one became my favorite narrow-band nebula filter, although again, the difference between it and the Lumicon UHC were fairly minor. Indeed, even the Orion Ultrablock seemed about on-par with the Lumicon UHC, so in these cases, I can recommend buying from one of these three based on price alone. However, that changed with the narrower "line" filters like the OIII. The Tele Vue OIII just didn't quite match the Lumicon OIII's performance, although it still provides a boost in contrast. The DGM OIII was pretty close to the Lumicon model in side-by-side tests, although I still like the Lumicon by a hair, so you really can't go wrong with either one of these two (ditto for the Thousand Oaks OIII Type 3). In fact, in my review tests of the DGM OIII, the DGM NPB narrow-band filter gave the DGM OIII a real run for its money in terms of the amount of contrast boost it provided. The Baader OIII was also good, but perhaps just a hair on the narrow side (cuts into the 4959 angstrom OIII emission line a bit), so again, I tend to fall back on the Lumicon OIII as continuing to be my "gold standard" in Oxygen III filters. These are not "anecdotal" accounts, but the result of some careful study, both spectroscopically and in the field with a slide comparative system. For those filters not on this "short list", well, "ya pays your money and ya takes your chances". I am still pretty confident that the Lumicon line is one of the best sets of filters out there. Clear skies to you.

I appreciate David sharing his observing experience. As a real scientist for 30 years and with far too many research Psychologist friends over the years I also appreciate that to quantify subjective measurements you need double blind tests, lots of data and statistics. If David had found outliers from his observations, in particular filters that were so much worse than the others that you probably shouldn't even consider them that might be somewhat useful. But one person's observations are still statistically meaningless.

Also hard factual observations such as "Orion put out many 2" filters with non-standard threads over the past several years that could sometimes be forced on but still fall on your mirror" and the current state of their threads would be useful. You sure don't want to take a chance on a used one.

As I said what we need to see in any filter comparison is first and foremost, transmittance spectra and secondly some ASTM testing on the durability of the coatings. Kind of a Consumers Reports on filters or say DxOMark.com for camera lenses. The transmittance spectra will tell you all you need to know about the filters and then you could have fun trying to correlate the data with observations.

I would also say that most consumers are not interested in the best filter no matter the cost but want to get the most value out of a filter. The best way to do this is compare transmittance spectra and some other things like durability and general build quality. What is the actual percent transmittance of the OIII lines and percentage of other visible light passed for Celestron OIII filter vs. the 4x more costly Lumicon OIII filter? That's what we really need to know.

The Celestron OIII filter appears to be the same as the Baader filter. The filter's maximum transmission is around 90% with a FWHM figure of about 85 angstroms (8.5 mm), somewhat narrower than the Lumicon OIII. There has been some reported variation in these figures from unit to unit, so with those variations comes variations in performance. In particular, the transmission of the 4959 Angstrom line is often less than 50%. That line is generally the weaker of the two in emission lines in many nebulae so this doesn't kill the filter's performance completely, but it may affect the amount of nebulosity seen depending on the particular unit you get. Clear skies to you.